Date of Award


Document Type

Master Thesis

Degree Name

Master of Engineering (Research)


School of Science, Technology, Engineering and Mathematics

First Advisor

Dr. Brendan O'Donnell

Second Advisor

Dr. Daniel Riordan


The imminent depletion of fossil fuels, as well as concerns for energy security and the obligation to respond to climate change has led to expanding worldwide popularity of Anaerobic Digestion (AD) of energy crops. Sugar beet is a popular AD feedstock due to its favourable characteristics; however it can be quite labour intensive requiring a range of specialist equipment to process the crop prior to undergoing AD. A crucial stage of this process involves the size reduction of beet by a mechanical chopper unit; this pretreatment breaks open the cellulose structure of the crop and increases the surface area available for attack by the microorganisms. This is reported to he highly beneficial in terms of increasing the biogas extraction rate. At present this process is typically conducted by chopper technologies which were primarily designed to coarsely chop beet for animal feed. The process also requires an operator to remain with the machine throughout the chopping operation. To thoroughly exploit the benefits associated with this mechanical pretreatment process, further development in this area is compelling.

This thesis, through collaboration with biogas machinery manufacturer Cross Agricultural Engineering LTD, explores ways of increasing efficiencies in the processing of beet feedstock. Developing upon current process methods, the research studies design possibilities for a new automated mechanical pretreatment unit capable of further reducing the beet chop size beyond conventional levels. Integral to the study, a lab scale experiment was conducted to determine biogas production rates from a range of chopped beet sizes. Tests were also conducted on beet processing machinery providing insight into the current energy balance in terms of direct input energy’ required to process beet feedstock and the resulting biogas energy yield. Analysis of the test results indicate that the current energy demand required for mechanical pretreatment of beet feedstock is less than that gained by the biogas energy yielded. These positive results gave confidence for development of new chopper prototypes which have potential to further harness beets energy’ potential. Each designs chopping ability’ was analysed and several modifications to the existing chopper concept are suggested, these new design features are expected to significantly enhance the biogas extraction rate from beet feedstock. Finally, a ladder logic program was also devised to facilitate automation of the machine concept proposed in this study. These valuable findings have the potential to aid biogas machinery manufacturers towards developing more efficient processing machinery.

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